[sdiy] 3340 VCO question - setting the lowest frequency

[Mattias Rickardsson]

On 10 September 2017 at 13:56, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> I’m reluctant to increase the cap value although in some ways that’s the obviously thing to do. Every single design I’ve ever seen for this chip uses the 1n value for the cap, and I’m not feeling confident enough to go against the opinion of every synth designer in history!

Oh, come on, Tom - do it! :-D

> But maybe none of those synths went this low? (It *is* sub audio, after all…)
> Does anyone have any experience to offer?

Not exactly experience, but the Memorymoog comes to mind... IIRC it
has 19 VCO chips where one is used as the LFO. Looking for the full
schematics (but actually not finding it, does anybody have it?) I
stumbled across this instead:

http://www.synthdiy.eu/files/Memorymoog%20Voice%20Modulation%20(from%20Tech%20Service%20Info%20p%2021).png

Oscillator 3 can apparently be switched down to low-frequent duties
using a larger capacitor, and the service documentation describes how.


/mr